Cook pasta as package directs for al dente pasta. Season shrimp with 1/4 teaspoon each of the salt and pepper. In large non-stick skillet over medium high heat, heat olive oil. Cook shrimp, stirring occasionally, until barely cooked through, 2 to 3 minutes. Stir in radishes and scallions; set aside; cover to keep warm. Drain pasta, reserving 1/2 cup of the pasta water. In pasta pot, combine heavy cream, cheese, Meyer lemon juice and zest, and remaining 1/2 teaspoon each of the salt and pepper. Add pasta and shrimp, toss gently. Add reserved pasta water to thin sauce, if needed. Serve sprinkled with dill.