Preheat the oven to 325°. In a bowl, toss the tomatoes with the garlic and 1 tablespoon of the olive oil; season with kosher salt and pepper. Transfer the tomatoes to one side of a parchment-lined baking sheet and lay the pancetta slices out on the other side. Bake for 25 minutes, until the pancetta is crisp. Transfer the pancetta to paper towels to drain, then crumble.
Roast the tomatoes for about 10 more minutes, until bursting and lightly caramelized. Transfer the tomatoes and any rendered fat from the pancetta to a bowl.
Meanwhile, in a small skillet, heat the remaining 1/4 cup of olive oil over moderately high heat. Add the sage and fry until bright green and crisp, 30 to 45 seconds. Drain the sage on paper towels; reserve the oil for another use.
Spread the ricotta on the toasts and top with the tomatoes and crumbled pancetta. Drizzle with olive oil, sprinkle with sea salt and pepper and top the toasts with the sage leaves. Serve immediately.
