In a bowl, mix together the olive oil, chili powder, cumin, paprika, salt, and pepper. Add the chicken breasts and coat them well with the marinade. Let marinate for at least 20 minutes (or up to 2 hours in the refrigerator).
Heat a grill or skillet over medium heat. Cook the chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F (75°C) and the chicken is cooked through. Remove from the heat and let rest for a few minutes before slicing.
While the chicken is cooking, prepare your base. In a separate bowl, combine the cooked quinoa or brown rice, black beans, corn, diced red bell pepper, and halved cherry tomatoes. Mix together and season with salt and pepper to taste.
In serving bowls, layer the quinoa/rice mixture. Top with slices of grilled chicken, avocado, and shredded cheese if using.
Sprinkle chopped cilantro over each bowl and serve with lime wedges and salsa or hot sauce on the side for an extra kick.
Notes
Feel free to customize with your favorite toppings.