Kittencal's Easy Tuna or Chicken Noodle Casserole

2 tablespoons butter

1 (10 3/4 ounce) can condensed cream of mushroom soup, undiluted

1/2-1 teaspoon garlic powder (or to taste, I use 1 teaspoon)

3 -4 tablespoons grated parmesan cheese

3/4 cup milk (or can use half-and-half cream)

1/2 cup sour cream (can increase to to 3/4 cup)

1/4-1/2 teaspoon seasoning salt (or to taste, or use white salt)

1/2 teaspoon fresh ground black pepper (or to taste)

1 small onion , finely chopped (can use 2 green onions)

1/4 cup pimiento , chopped

1 small green bell pepper , finely chopped

1 large celery rib , diced

1 (6 1/2 ounce) can tuna , drained and flaked (can add another 3 ounces for a more meatier casserole if desired, or use cooked chicken or turkey)

12 -15 butter flavored crackers, broken in pieces (such as Ritz Crackers)