Preheat oven to 450 F.
Toss the tomatoes with the oil and spread out onto a baking sheet, cut side up. Add the garlic into the cavities of the tomatoes, drizzle with balsamic and add a pinch each of salt and pepper. Lightly press the tomatoes down to flatten.
Roast until the tomatoes soften and caramelize, about 20-30 minutes. Allow them to cool completely, then carefully remove and discard the skin.
Meanwhile, add the beans, avocado, lemon juice, parsley, basil, garlic, salt and pepper to a food processor and puree until smooth.
Once the tomatoes are finished, brush the bread with the remaining oil and toast on the baking sheet in the hot oven until lightly golden brown, about 5 minutes.
To assemble, divide the avocado between the four slices of toast, top with a piece of roasted tomato and garnish with the fresh basil leaves and fleur de sel.