Cook vegetables until tender but still slightly crunchy to maintain good texture., Use high-quality Parmesan cheese for best flavor., Vegetable swaps like zucchini noodles can be used but watch cooking times to avoid sogginess., Watch broiler carefully during broiling to prevent burning., Vegetables and sauce can be prepared up to 24 hours in advance and refrigerated; add tuna and bake fresh when ready., Store leftovers in an airtight container in the refrigerator up to 3 days; reheat gently in oven at 350°F for 20-25 minutes., Freeze casserole up to 2 months in freezer-safe containers; thaw overnight in fridge and reheat in oven until warmed through., To prevent watery casserole, simmer sauce mixture longer or add more Parmesan or keto-friendly thickener if needed., Protein swaps include shredded rotisserie chicken or canned salmon., For added flavor, try herb variations such as replacing dill with thyme, oregano, or parsley., Adding veggies like sautéed mushrooms or bell peppers increases nutrition and flavor., For a spicy twist, add diced jalapeños or hot sauce., Top with crunchy additions like toasted almond slivers or crushed pork rinds before broiling., Can be served cold as a creamy salad for warmer days or lunches.