Preheat oven to 350.
Heat oil in a skillet on the stove and cook meat, onion, celery, and garlic.
Stir in tomato paste, and season with salt & pepper to taste.
If not using an oven-safe skillet, transfer meat mixture to a medium-sized casserole dish.
Heat up cauliflower in microwave according to package instructions, and drain if any excess water.
Place cauliflower in a food processor.
Add in cheeses, cream, butter, and oregano.
Process until mixture has a "mashed potato" consistency.
Spread mixture on top of meat evenly.
Place in 350 degree oven for about 30 minutes, until top is golden brown.
Cut and serve warm.