To food processor, add peas, walnuts, basil, garlic, zest of half a lemon, juice of whole lemon, and olive oil. Blend, scraping down sides of bowl as needed, until textured but creamy and well combined. Taste and adjust seasoning with salt. Dollop basil mixture over whipped feta, running a knife lightly through mixture to marble the two dips together. Garnish with extra peas and basil leaves, if desired. Serve alongside crackers and vegetables for dipping.