Step 1. Cook the rice: In a saucepan, bring water to a boil, add rice and a pinch of salt, reduce heat to low, cover, and cook for about 18 minutes or until water is absorbed and rice is tender. Remove from heat and let it sit, covered, for 5 minutes. Fluff with a fork and set aside to cool slightly.
Step 2. Prepare the beans: Rinse and drain black beans. In a small pot, heat a teaspoon of olive oil over medium heat. Add minced garlic and sauté for about 1 minute until fragrant. Add black beans, cumin, chili powder, and a bit of water. Cook for 5-10 minutes until beans are warm and flavors are mingled. Season with salt and pepper to taste.
Step 3. Prepare vegetables: Chop cherry tomatoes, red onion, avocado, and lettuce. Slice lime into wedges. Finely chop cilantro. If using, slice jalapeño thinly.
Step 4. Assemble the bowl: In each bowl, lay a foundation of rice, and top with black beans, corn, chopped vegetables, and lettuce. Add a spoonful of sour cream and sprinkle with shredded cheese and cilantro. Serve with lime wedges on the side for squeezing over.