Saute': In a large frying pan, combine olive oil and chopped onion, cooking on med-high heat stirring frequently until translucent. 3-5 minutes
Add choice of meat, salt, pepper and Montreal seasoning: To the pan with the onions, cooking until browned and no longer pink making sure to stir frequently to make a crumble like mixture. Drain excess liquid or grease into a separate heatproof container, cool and discard.
Boil the cauliflower: Place cut-up cauliflower in a medium pot, add choice of broth and enough water to cover. Bring to a boil and reduce to a simmer until fork tender.
Mash the cooked cauliflower: When cauliflower is fork tender, drain liquid, reserving liquid in a separate heat proof bowl.** Add 4 Tbsp of butter to drained cauliflower, mash with potato masher, then and add garlic, salt & pepper to taste.
Add: 1/4 Cup of reserved cauliflower broth to meat mixture and stir well. **(Keep remaining cooled broth up to 4-5 days in refrigerator for soup. Or put in a freezer safe bag or container and freeze up to 3 months for future use)
Cook frozen mixed vegetables: Follow cooking directions on steamed mixed vegetables package or if using canned version, drain liquid before using.
Preheat oven: to 375 degrees
Grease: 8 x 13 casserole dish lightly with olive oil or cooking spray
Layer: Spread even layers of meat mixture, then top with mixed vegetables. Lightly salt and pepper before adding mashed cauliflower in greased casserole dish. Note: Canned vegetables have plenty of salt, even low sodium varieties so season carefully.
Sprinkle cheese: Sprinkle with grated cheese evenly over the top of mashed cauliflower layer.
Bake in oven: Place casserole dish uncovered in preheated 375 degree oven and bake for 30 minutes until heated through and cheese is golden brown.
Remove from oven: Sprinkle with green onions and serve.