Vegan Burrito Bowls Loaded with Veggies

Name: Vegan Burrito Bowls Loaded with Veggies
Ingredients: 1 small red onion (diced); 2 cloves garlic (minced); 1 zucchini (diced); 1 yellow squash (diced); 1 cup frozen corn (kernels removed); 1 red pepper (diced); 2 tsp cumin; 1 tbsp chili powder; 15 oz can of black bean (rinsed and drained); 1/4 tsp salt; 1/4 tsp pepper; 3/4 cup vegetable stock (divided); 2 cups brown rice; 4 cups water; 2 tbsp cilantro (roughly chopped); 1 cup tomatoes (diced); 1 avocado (diced); 1 lime (cut into wedges); 2 cups shredded lettuce