Combine the garlic powder, chili powder, paprika, salt, and pepper in a small bowl.
Prepare grill for direct heat and preheat to medium. Oil the grates.
Remove the outer leaves from the heads of the cauliflower and trim the stem so it sits flat (be careful not to cut too much of the stem). Place stem side down on a cutting board and slice about 1/3 off each side – reserve for another use. Slice the rest of the cauliflower into 3 equal slices, about 1 inch thick.
Lay the steaks flat and brush with olive oil on both sides and sprinkle the spice mixture evenly on both sides.
Grill 5 minutes per side with the lid closed.
Heat the queso, drizzle some over the cauliflower steaks, and serve the rest on the side. Top with salsa and garnish with cilantro leaves.