Preheat oven to 350 F.
In a medium pot, boil sweet potato cubes until soft; approx. 10-15 minutes (depending on the size of your cubes).
While sweet potatoes are boiling in a large pan and saute onions and celery until translucent; 3-5 minutes. Add ground turkey and garlic; brown and season with garlic salt, salt & oregano. Add green beans, zucchini, squash and tomato sauce. Heat throughout.
Once potatoes have softened, drain all water and mash with a potato masher, hand held immersion blender, or hand mixer.
Spoon meat mixture into the bottom of a casserole dish and cover with prepared mashed potatoes. Sprinkle with shredded cheese and bake for 10-15 minutes until cheese is melted.
Adapted from Healthy Sweet Potato Shepherd's Pie