Have the asparagus, carrots, zucchini, and yellow squash cut up and ready. Set these vegetables aside. Bring the chicken broth and water just to a simmer in a medium saucepan; keep warm.
Heat 1 tablespoon each olive oil and butter in a large saucepan over medium heat. Add 1/2 cup minced onion and the minced garlic; cook 3 minutes. Add asparagus and carrots; cook 2 minutes. Add zucchini and yellow squash; cook until just tender, about 2 minutes more. Transfer to a bowl and set aside.
Heat 2 more tablespoons olive oil in same sauce pan over medium heat. Add 1/2 cup more minced onion and cook 3 minutes. Add the arborio rice (or short-grain rice), stirring to coat. Stir in the dry white wine and cook until almost absorbed, 2 to 3 minutes. Add 3/4 cup reserved broth and cook, stirring constantly, until almost absorbed. Simmer, adding broth 1/2 cup at a time, stirring constantly until broth is absorbed before adding more, about 20 minutes. Rice will be creamy and just tender.
Stir in 2 more tablespoons butter, 2 tablespoons Parmesan cheese, salt, pepper, chopped mint, grated lemon peel, peas, and reserved vegetables.
Serve with additional Parmesan cheese.