Preheat oven to 400 degrees.

Line a rimmed baking sheet with parchment paper, and spray with non-fat cooking spray. Place whole tomatoes and garlic on baking sheet and roast in oven for about 30 minutes.

Meanwhile, set a large sauce pan over medium high heat, melt butter and add in onions and salt. Cook until unions become tender and translucent, about 5 minutes.

Dump the cooked tomatoes and garlic cloves into the pot with the onions.

Add in basil, stock, pepper and oregano, and stir to combine. Bring mixture to a simmer, and then lower heat to medium low and let cook for about 15 minutes.

Remove from heat and stir in ricotta cheese. Now, using an immersion blender, puree the soup until smooth. Season with additional salt and pepper as needed.

Pour soup into 8 individual ramekins or oven safe bowls. Slice fresh mozzarella into 8 equally sized slices, and top each bowl of soup with a slice of mozzarella.

Place ramekins under broiler until mozzarella melts and begins to bubble. Remove from oven and serve.