Stew the spinach in a pan with the garlic. Season the cream cheese with salt and pepper and refine the spinach with it.
Put the spinach and cream cheese mixture in a baking dish and pour the drained tuna over it. If you like, you can also add tomatoes and mushrooms. If you like, season everything again and then sprinkle with the cheese.
Bake the casserole in the preheated oven for 25 minutes at 200 ° C top / bottom heat.