Preheat your grill or oven to 400°F (200°C).
In a small bowl, mix together 2 tablespoons of olive oil, garlic powder, onion powder, smoked paprika, salt, and black pepper.
Brush the mixture evenly over the top and inside of each portobello mushroom cap.
Place the mushrooms on the grill or a baking sheet if using the oven, gill side up.
Sprinkle the shredded cheddar cheese and crumbled bacon evenly over each mushroom.
Drizzle the remaining 2 tablespoons of olive oil over the stuffed mushrooms.
Grill or bake for 15-20 minutes, or until the mushrooms are tender and the cheese is melted and bubbly.
Remove from heat and garnish with chopped parsley before serving.