Heat the oven to 375°F.

• In a strainer, rinse the white beans.
• Zest and juice the lemon, keeping the zest and juice separate.
• Finely chop ¼ cup of the arugula.
• Strip the thyme leaves from the stems.

In a medium bowl, combine the white beans with the lemon zest, chopped arugula, thyme, and 2 teaspoons oil. Using a fork, coarsely mash the white bean mixture. Stir in the ricotta, then season to taste with salt and pepper.

On a sheet pan, lightly drizzle both sides of the pitas with oil and sprinkle with salt. Spread the white bean mixture on top of the pitas and bake until the pitas are crisp and the ricotta is browning around the edges, 20 to 25 minutes. While the pizzettas cook, make the citrus salad.

• Using a sharp knife or your hands, peel the grapefruit and orange. Cut the citrus in half lengthwise, then crosswise into ¼-inch-thick half-moons. Discard any seeds.
• Coarsely chop the olives.
• Strip the mint leaves from the stems; coarsely chop the leaves.

In a medium bowl, combine the grapefruit, orange, olives, and mint and stir to mix. Season to taste with salt and pepper.

• Coarsely chop the walnuts.

In another medium bowl, combine the walnuts with the remaining arugula, 2 teaspoons oil, and 1 to 2 teaspoons lemon juice. Toss to coat, then season to taste with salt and pepper.

Transfer the pizzetas to individual plates and top with the arugula and walnuts. Serve with the citrus-olive salad on the side.