Crack the egg into a large bowl and lightly whisk. Add the ground chicken, 1/2 cup Parmesan, basil, panko, lemon zest (save the juice for later!), and 3/4 teaspoon salt to the bowl. Use your hands to thoroughly combine. Roll chicken mixture into about 10 meatballs, each a little larger than a golf ball. The mixture will be sticky and wet; if you need to, wet your fingers between meatballs to prevent sticking.
Warm 1 tablespoon oil in a 10-inch nonstick skillet or pan over medium-high heat and swirl it around to coat the pan. Use tongs to sear the meatballs for about 2 minutes per side on three sides. They will start to look a bit like triangles after you sear them, but don’t worry, they’ll round back out as they cook. The meatballs will not be entirely cooked at this point—you’re just getting a nice golden brown sear on the outside.
Scoot the meatballs to the outer edges of the pan to make a clearing in the center. Add the chicken stock, orzo, garlic, lemon juice, and remaining 1/4 teaspoon salt to the center of the pan and stir to combine. The meatballs, orzo, and chicken stock will all mix together in the pan, just be sure to spread the orzo out evenly so that it’s covered in liquid.
Raise heat to high to bring mixture to a boil, then reduce heat to medium-low and stir often until all liquid is absorbed and orzo is tender, 10 to 15 minutes, adding the peas and Parmesan for the last minute of cooking. The orzo should be the consistency of risotto, not too thick, not too thin. If it gets too thick, just add another splash of chicken stock or water. If it looks too thin, keep cooking.
Garnish with fresh basil and serve with additional Parmesan and lemon wedges.