Step 1

Preheat oven to 350°. Toast pistachios on a rimmed baking sheet, tossing once, until golden brown, 5–8 minutes. Let cool, then finely chop. Reduce oven temperature to 325°.

Step 2

Slice about ½" off the top of each tomato; reserve tops. Using a spoon, scoop out the center of each tomato (save for making sauce). Season insides of tomatoes with salt and pepper. Transfer to a baking dish large enough to hold tomatoes (they can be snug).

Step 3

Mix pistachios, garlic, raisins, ¼ cup oil, and 1 Tbsp. thyme in a medium bowl; season with salt and pepper. Place about 1 Tbsp. filling in each tomato. Tear mozzarella into bite-size pieces and snuggle into tomatoes. Top with remaining filling (you may need to gently press filling down with your fingers).

Step 4

Replace tomato tops; drizzle with oil. Scatter thyme sprigs over and bake, uncovered, until tomatoes release some liquid and begin to get a little wrinkly on top, 35–45 minutes. Let cool slightly before serving.