Heat up oil.

Chop the onion

Put onion in oil and stir until slightly brown

Cut up tomatoes, garlic, and leek

Put the three and a pinch of salt in with the onion. Sauté the ingredients until the tomatoes are slightly soft

Squeeze lemon juice over mixture

Add the basil

Spray a baking sheet and place the mushroom bottom side up

Add the ingredients into the mushroom and top with cheese

Bake for 12 minutes on 400