Preheat the oven to 425 degrees F. Toss the bell peppers, fennel, red onion, 2 tablespoons olive oil, 1/2 teaspoon salt and a few grinds of pepper on a rimmed baking sheet. Bake, stirring occasionally, until the vegetables are tender and lightly browned, about 25 minutes.
Meanwhile, bring a large pot of salted water to a boil. Add the tortellini and cook as the label directs; drain. Put the kale in a large bowl and top with the warm tortellini and roasted vegetables.
Heat the remaining 1/4 cup olive oil in a small skillet over medium heat. Add the garlic and cook, stirring occasionally, until it just starts browning, about 2 minutes. Remove from the heat and add the vinegar; pour over the tortellini mixture and toss to coat. Add the basil and fennel fronds, season with salt and pepper and toss.