Remove fava beans from pods. Bring a pot of water to a boil, and submerge beans for 1 minute, then drain and chill in cold water. Slit translucent skin of each bean and discard. Test a bean for tenderness: if hard, simmer for 2 to 8 minutes, until tender. Cover and refrigerate until needed, up to 2 days.

Pour broth into a saucepan, bring to a simmer and keep warm. Place a heavy-bottomed pot or Dutch oven and a large skillet on stove. Divide butter or oil, garlic and shallots between the two pans.

Place Dutch oven over medium heat and sauté garlic and shallots until translucent. Add rice and stir for 2 minutes. Add wine and lemon zest and continue stirring until all the wine is absorbed. Begin stirring in the broth, one ladleful at a time, allowing each addition to be absorbed before adding the next. Meanwhile (after about the second ladleful of broth), place skillet over medium-high heat. Stir until garlic is light gold. Add zucchini and sauté 2 to 3 minutes. Remove from heat and set aside.

When most of the broth is incorporated, taste rice; it should be creamy with a slightly firm center. Remove from heat and mix in cheese. Cover and allow to rest for 1 minute. Meanwhile, return zucchini mixture to medium heat. Add favas and season with salt and pepper to taste. Stir just until mixture is warm, then remove from heat.

Add half the basil to zucchini and mix gently. Stir remaining basil and lemon balm or lemon juice into risotto. Place a portion of each on plates and serve immediately.