Pat steak dry with paper towels. In a small bowl, mix chili powder, cumin, garlic powder, salt, and pepper. Rub half the spice mixture all over the steak slices. Toss peppers and onion with remaining 1 tbsp olive oil and the rest of the spice mix.

Heat 1 tbsp olive oil in a large skillet over high heat until smoking. Add steak in a single layer (work in batches if needed). Sear 2-3 minutes without moving, until deeply browned. Flip and cook 1-2 minutes more for medium-rare. Transfer to a plate and tent with foil.

Add peppers and onion to the same skillet. Cook over medium-high heat, stirring occasionally, until softened and charred in spots, 6-8 minutes. Return steak and any juices to the pan, toss briefly to combine, then remove from heat.

In a separate medium skillet, melt butter over medium heat. Add cauliflower rice and cook, stirring occasionally, until tender and lightly golden, 5-7 minutes. Season with salt and stir in lime juice off heat.

Divide cauliflower rice among 4 bowls. Top with steak and pepper mixture. Add avocado slices, a dollop of sour cream, salsa, and a sprinkle of cilantro. Serve immediately with extra lime wedges if desired.