Cook the brown rice. Rinse the rice, then cook according to package directions. Fluff with a fork, season with a pinch of salt, and set aside.
Sauté the veggies. Warm olive oil in a skillet over medium heat.
Add onion and bell pepper, a pinch of salt, and cook 4–5 minutes until softened.
Season and heat the beans and corn. Stir in black beans, corn, cumin, chili powder, and smoked paprika. Cook 2–3 minutes until warmed through. Adjust salt and pepper.
Warm the tortillas. Heat each tortilla in a dry skillet for 15–20 seconds per side until pliable, or wrap them in a damp towel and microwave for 30 seconds.
Set up your assembly line. Arrange rice, bean mixture, avocado, salsa, cheese, lettuce, and cilantro so you can build quickly.
Assemble. Lay a tortilla flat.
Add a base of rice, a generous scoop of beans and corn, a few avocado slices, a spoon of salsa, and any cheese or lettuce. Squeeze a wedge of lime over the filling.
Roll it up. Fold the sides in, then roll from the bottom up, keeping the filling snug. If you like it crisp, place the burrito seam-side down in a warm skillet for 1–2 minutes to seal and lightly toast.
Serve. Slice in half if you want and add extra salsa or hot sauce on the side.