Preheat oven to 350 F. Spray a 9×13 casserole dish with nonstick cooking spray. Set aside.
Ribbon cut or spiralize the zucchini into noodles. Press/squeeze out as much excess water as possible (see notes). Set aside.
In a large bowl, mix together the drained tuna, mayo, green chiles, chives, mustard, seasoning salt, garlic powder and black pepper. Set aside.
Heat a large skillet on medium heat. Add the onion, celery and chili powder. Sauté 5 minutes or until onions begin to brown.
Whisk coconut flour and milk into the celery and onion mixture until smooth or very few flour clumps remain.
Add zucchini noodles to the skillet and toss together. Cover and cook for 1-2 minutes on medium heat until zucchini is softened but not thoroughly cooked.
Remove skillet from the heat and pour contents into the tuna/green chiles mixture combining well.
Pour mixture into the prepared casserole dish and bake for 15-20 minutes or until edges are browned. Optional- broil casserole 1-2 minutes for crispier edges.
Garnish with fresh herbs and top with optional lemon slices.
