Preheat oven to 450F.
While oven is preheating, brush mushroom with olive oil, sprinkle with garlic powder, paprika, & salt & pepper.
Once oven is preheated, place mushroom and red pepper directly on rack. Place cookie sheet below to catch any dripping juice.
Cook portobello about 15-20 minutes before removing, cook red pepper about 30 minutes, or until skin is black and blistering.
After removing red pepper, place in a glass bowl with lid, or plastic wrap covering the top. This steams the red pepper, making the skin easier to remove.
Once red pepper has cooled enough to handle, remove skin by rubbing/pulling with fingers.
Butter the outside of each slice of bread, spread mayo on the inside of each slice.
Place slices of roasted red pepper (I used half the pepper), slices of portobello mushroom, chopped basil, and enough goat cheese to cover the sandwich (about 60 grams in my case). Add more salt & pepper is desired.
In a pan on medium heat with a lid, cook grilled cheese until browned and cheese is melting.