In a small bowl, whisk together the mascarpone, Greek yogurt, honey, lemon zest, and lemon juice until completely smooth, airy, and creamy.
Add the diced melon, finely chopped prosciutto, and basil. Gently fold everything together just until combined, keeping the mixture light and intact.
Taste and adjust if needed - a tiny extra squeeze of lemon juice can brighten the flavor if the melon is very sweet.
Place a 4-inch ring mold on a serving plate. Spoon the mixture inside and gently press with the back of a spoon to shape into a clean cylinder.
Carefully lift the mold to reveal the tartare. Garnish with torn prosciutto, roasted pine nuts, and fresh basil.
Serve immediately for the best texture and presentation.