Preheat oven to 435F. Slice tomatoes into 1/4" slices and drizzle with olive oil. Season with salt and pepper to taste.
Roast tomatoes for about 30-40 minutes. You can poke small holes through the tomato using toothpicks to minimize "steaming" effect.
Preheat oven to 350F. Combine all of the Tart Base ingredients in a food processor by pulsing slowly until a dough forms.
Press dough into thin layers (about 1/4" - 1/2") using silicone cupcake molds. You should get 12 total tarts from this.
Bake the dough for 17-20 minutes or until it's hardened, then remove from the oven and let cool completely.
Tap the bottom of the silicone cupcake mold to remove the tart from the mold.
Caramelize the onion and garlic in 2 tbsp. olive oil in a pan over high heat.
Assemble tarts with tomato, caramelized fillings, fresh thyme, and crumbled goat cheese over the top.
Bake tarts at 350F for about 5-6 minutes or until cheese begins melting. Remove and serve hot.