Add ground beef to a skillet and season with salt. Cook over medium-high heat, breaking up and stirring to brown. Set aside.
Preheat oven to 400 degrees.
Add poblano pepper and onion to a small baking sheet and drizzle with olive oil. Cook for 5-8 minutes or until peppers and onions soften. Remove to a cutting board and cool slightly. Dice vegetables.
Lower oven temperature to 375 degrees.
Place butter into a saucepan and place over medium heat. Whisk in minced garlic and cook 1 minute. Whisk in flour, salt and ground chipotle. Cook 2 minutes, whisking constantly. Add milk, sour cream and 2 cups of shredded cheese. Stir until cheese is melted and sauce has thickened. Stir in peppers, onions.
Spray a 9 x 13-inch baking dish with non-stick spray.
Add ground beef, black beans and rice to baking dish. Pour cheese sauce over and stir to until well combined. Top with remaining 1 cup of shredded cheese.
Bake for 25 minutes or until mixture is heated through and cheese is melted.
Serve with cilantro, lime, avocado, fresh tomatoes and sour cream.