Preheat the oven to 425 degrees F.
Cut the cauliflower head in half. Then slice each of those halves lengthwise into 3/4-inch-thick steaks. (The slices further from the center stem will break apart into smaller pieces, and that is ok.) Arrange them in a single layer on a sheet pan.
In a small bowl, whisk 3 tablespoons olive oil, smoked paprika, cumin, onion powder, 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper.
Drizzle the oil-spice mixture on the cauliflower, brushing it all over, so the cauliflower is well-coated.
Roast for 25-30 minutes, flipping just over halfway through roasting, until the cauliflower is browned on the edges.
For the pesto, combine the roasted red peppers, garlic, almonds, Parmesan, 1/4 teaspoon kosher salt and 1/4 teaspoon black pepper in a food processor or blender. Finely chop the ingredients. With the motor running, drizzle in 1/4 cup olive oil through the feeder tube, processing until the pesto is pureed and combined.
To serve, spread pesto on a plate and arrange the cauliflower steaks on top. Sprinkle with parsley and chopped almonds.