Toss the carrots, leeks, potatoes and fennel with the olive oil in a 6- to 8-quart slow cooker. Add 5 cups water, the tomatoes, parmesan rind, 2 tablespoons pesto, 1/2 teaspoon salt and a few grinds of pepper. Cover and cook on high until the vegetables are tender, 7 to 8 hours.
Uncover and stir in the beans and ditalini. Cover and continue cooking on high until the pasta is al dente, about 15 minutes. Remove the parmesan rind. Stir in the remaining 1 tablespoon pesto and season with salt and pepper. Top each serving with more pesto, the parmesan and fennel fronds. Serve with the focaccia.