It's also easily adaptable to what you have in the house.
Some suggestions for substitutes:
Salsa or chutney for the marinara
Rice or millet for the quinoa
Artichoke hearts, roasted red peppers, sauteed onions, corn, beans, diced tomatoes, pickled jalapenos for the olives
Any kind of melty cheese for topping- swiss, cheddar, muenster, monterey jack. Feta and goat cheese are also super tasty mixed into the filling.
You see where I'm going here- the options are endless! You could even get really crazy and try an Indian-inspired stuff pepper and add garam masala and some golden raisins the filling! Maybe mix in a little prepared korma sauce- I die!
This version is Italian-inspired with the pepper jack cheese adding some Mexican flair- bringing a little fusion to BettyCupcakes!
My latest cast of characters: yellow bell peppers, nutritional yeast, olives, quinoa, marinara sauce, basil, ground black pepper, and pepper jack cheese. Not pictured- red pepper flakes, a last minute addition. You know me- I like to keep things spicy up in here!There's no picture of this step because it's boring, but start your quinoa over medium heat. Oh, and preheat your oven to 400.
In a medium bowl, mix your marinara sauce, nutritional yeast, red pepper flakes, basil, and ground black pepper. Skip the salt- the olives add plenty!
Slice up some olives or other filling items.
Stir 'em into the saucy mixture.
Grate up some cheese and toss it in, too. Set aside. 
Time to hollow out those peppers. Grasp firmly and insert knife at the top, about an inch. Move the knife around in a circle creating a hole. You want to take off the stem and a bit of the ribs. Pretend it's a pumpkin. 
If your bell pepper is wobbly, just slice a bit off the bottom to make things even stevens.
Place into a loaf pan.
The quinoa's cooked now. Please ignore the thermometer- we've been sharing some nasty bugs this winter! All better for now (knocking on wood as we speak).
Add two to two and a half cups of the cooked quinoa to the sauce mixture. Taste and add quinoa, if desired. 
Fill up your peppers. Really get the mixture in them and then overfill by a bit. Don't skimp!
Top with more cheese. (Is anything in this world not made better by the addition of cheese? Chew on that nugget, kids.)
Bake at 400 until peppers are soft and cheese is melty and browned ~ 25 minutes. Side suggestion- roasted broccoli. Delish!
Stuffed Peppers
serves 2
2 large bell peppers
1 cup quinoa, rinsed
2 cups water
1/2 cup marinara sauce
2 tbsp nutritional yeast
1 tsp dried basil
1/4 tsp black pepper
1/4 tsp dried red pepper flakes, optional
10 kalamata olives, sliced
2 oz. jalapeno pepper jack cheese, shredded
Preheat oven to 400.
Cook rinsed quinoa in the water until done- approximately 20 minutes. Set aside.
In a medium bowl, combine marinara sauce, nutritional yeast, basil, black pepper, red pepper flakes, olives, and half of the cheese. Stir well. Set the rest of the cheese aside.
Add 2 to 2 1/2 cups of the cooked quinoa to the marinara mixture and stir well to combine. Taste and add more quinoa if desired. Otherwise, save the remainder of the cooked quinoa for another recipe.
Hollow out the peppers by cutting around the stem. Remove the stem and carefully remove any large ribs inside while leaving the pepper whole. Cut a small slice off the bottom, if needed, to make your pepper level so it won't tip over while baking.
Fill peppers with quinoa mixture to the brim; overfill just a bit. Top with the remaining cheese.
Bake at 400 for 25 minutes, until cheese on top is browned and peppers are tender.
