Preheat the oven to 350 degrees F. Spread a little butter on the bottom of a 9-by-13-inch baking dish.
Heat some butter in a large skillet over medium-high heat. Add the peppers and onions and cook until softened, about 4 minutes. Off heat, add the tequila, then return to the heat and cook until evaporated, about 1 minute. Add the chili powder, garlic, jalapenos and some salt and pepper and cook for a minute or 2. Add the beans to the skillet and stir to combine everything. Cook until warmed through, about 4 minutes.
Spread half of the beans in the prepared baking dish. Top with half of the Cheddar and pepper Jack cheeses. Spread on the remaining beans and top with the remaining cheese. Bake until the cheese is melted and just beginning to brown, 20 to 25 minutes.