Add corn to grill and cook, turning occasionally, until cooked through and charred, about 10-12 minutes; let cool before cutting the corn kernels off the cobs.
Melt butter in a large skillet over medium high heat. Add corn, jalapeño, and garlic. Cook, stirring occasionally, until corn is heated through and jalapeno is tender, about 3-5 minutes. Stir in mayonnaise, cotija, cilantro, chili powder and lime juice; set aside.
To make the pico de gallo, combine tomatoes, red onion, cilantro, garlic, lime juice and salt in a medium bowl; set aside.
In a large saucepan of 2 cups water, cook rice according to package instructions.
Divide rice into bowls. Top with corn mixture, pico de gallo, romaine, black beans and avocado.
Serve immediately, garnished with cilantro and lime, if desired.