Thinly slice the onion and halve the mushrooms.

In a plastic bag, mix breadcrumbs and yogurt to soften. Add ground meat and remaining meat mixture seasonings. Knead well and cut the tip of the bag to form meatballs.

Heat salad oil in a pan over medium heat. Squeeze out meatballs and cook until browned. Add onion and mushrooms, sauté until the onion softens. Add flour and stir until no longer powdery.

Add cooking sauce ingredients, bring to a boil, cover, and simmer on low heat for 7–8 minutes until the meatballs are cooked and the sauce thickens. Stir in mustard.