Spray large, nonstick baking sheets with cooking spray. Set aside.
Cut bell peppers into 2×1-1/2-inch strips; cut strips into bite-size triangles. (Each bell pepper strip should yield 2 or 3 triangles.)
Spray large, nonstick skillet with cooking spray. Add tomatoes, onion, chili powder, and cumin. Cook over medium heat 3 minutes or until onion is tender, stirring occasionally. Remove from heat. Stir in rice, Monterey Jack cheese, cilantro, and pepper sauce.
Top each pepper triangle with approximately 2 tablespoons rice mixture; sprinkle with Cheddar cheese. Place on prepared baking sheets; cover with plastic wrap. Refrigerate up to 8 hours before serving.
When ready to serve, preheat broiler. Remove plastic wrap. Broil nachos, 6 to 8 inches from heat, 3 to 4 minutes (or bake at 400°F 8 to 10 minutes) or until cheese is bubbly and rice is heated through. Transfer to serving plate and garnish, if desired.