Heat water and 1 teaspoon salt (or to taste) in a saucepan over medium heat until steaming; keep warm.
Melt 2 tablespoons butter in a large Dutch oven or pot over medium-high heat. Add the onion and cook, stirring occasionally, until softened, 2 to 3 minutes. Then add the rice and garlic; cook, stirring until toasted, 2 to 3 minutes.
Pour in the salted water and bring to a boil, reduce to a simmer, cover, and cook for about 15 minutes on medium heat, stirring frequently.
Reduce the heat to low and stir in the peas, ham, mustard, Parmesan cheese, and remaining 2 tablespoons butter. Cook for another few minutes, stirring until the liquid is absorbed and the risotto is at desired consistency.
Serve with additional Parmesan cheese, pea shoots, or microgreens. You can also add fresh herbs like parsley or fresh mint.