Split the yellow squash and zucchini lengthwise down the middle. Brush them and the corn with olive oil, sprinkle with salt and pepper and grill until the veggies are somewhat soft and have nice grill marks. Allow to cool slightly, then cut the squash and zucchini into large dice. Scrape the corn from the cob.
Warm the tortillas in a microwave. Heat the black beans in a pot and mash with a fork.
To build the burritos, heap some Garlic Cilantro Lime Rice, mashed beans and diced veggies in the middle of each tortilla. Top with grated cheese, chopped tomatoes, chopped onions and sour cream. Tuck in the ends and roll into a burrito shape.
Garlic Cilantro Lime Rice:
Heat the oil in a large skillet over medium heat. Add the garlic and onions and cook for 3 to 4 minutes. Reduce the heat to low and add the rice and salt. Cook over a low heat for 3 minutes, stirring constantly to make sure the rice doesn't burn. Add 2 cups of the broth and the juice and zest of 2 limes and bring it to a boil. Reduce the heat to low, cover and simmer for 10 to 15 minutes or until the rice is done. Add more liquid as needed. The rice shouldn't be sticky.
Just before serving, stir through the juice of 1 lime and lots of chopped cilantro.