1. Cut asparagus into 1-inch pieces, discarding tough ends. Cut snap peas in half.
2. Stir together ricotta, lemon juice, 1 tsp. zest, and 1/4 tsp. salt in a medium bowl.
3. Bring 4 qt. water to a boil in a stockpot over high heat. Add 1/4 cup salt; return to a boil. Add pasta; boil, stirring occasionally, 11 minutes or until al dente. Add asparagus and sugar snap peas, and cook 2 to 3 minutes or until tender. Drain pasta mixture, reserving 1/4 cup pasta water. Return pasta to pot. Stir in olive oil, radishes, and reserved pasta water.
4. Spread half of ricotta mixture in serving dish; top with pasta mixture. Dollop with remaining ricotta mixture. Sprinkle with mint and remaining zest. Add pepper to taste. Serve immediately.