In a small bowl, whisk together chili powder, 2 teaspoons oil, sugar, salt and pepper. In a baking dish, coat steak with spice mixture.
To make polenta, combine milk, water and cornmeal in a large saucepan over low heat. Cook, stirring occasionally, until polenta is creamy, 25 minutes. Season with salt.
Heat grill pan over medium-high heat. Toss peppers with remaining oil and cook until charred and soft, 5 minutes. Transfer to a plate and add steak to pan. Grill 5 to 7 minutes per side, or until it reaches the desired doneness. Transfer to a foil-lined cutting board and let rest 5 minutes, then thinly slice across the grain.
In a small bowl, combine avocado and lime juice and season with salt.
Divide polenta among four bowls and top with beans, steak, peppers and avocado.