In food processor fitted with steel blade attachment, pulse together feta cheese and yogurt, scraping down bowl as needed, until smooth and creamy. Transfer to large plate, spreading over bottom of plate to cover. Set aside and wipe out food processor.

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.