Mushrooms with vegetables in sweet and sour sauce. Very tasty and easy!

Ingredients:
Mushrooms - 300 g.
Onions - 1 pc.
Sweet yellow pepper - 1/2 pc.
Sweet red pepper - 1/2 pc.
Pepperoni - 1/2 pc. (on request)
Garlic - 1 clove
Parsley
Sauce:
Brown sugar - 1 tsp
Soy sauce - 2 tablespoons
Rice vinegar - 1 tablespoon
Ketchup - 1 tablespoon