Place a large pot filled with salted water on stove and bring to a boil. Cook orzo to box directions. Drain and return to cooled pot and add the olive oil. Stir to combine and let cool. Add pesto and stir to combine.
Sauté the onion and carrots on medium high heat in 2 tbsp butter for 5-6 minutes, until soft and starting to brown. Add corn, a little salt and pepper, stir to combine and sauté 3-4 minutes. Remove corn mix from the pan and set aside. Add remaining butter in sauté pan followed by the zucchini, squash and peas. Cook 5-6 minutes, stirring occasionally but not continuously so the veggies brown a bit. Add garlic and adjust seasonings to taste with a little more salt and pepper. Sauté an additional 2-3 minutes to allow the garlic to cook and mellow a bit.
Mix all veggies with the pesto orzo, add the chopped basil and chives and squeeze lemon over the top. Toss to combine all ingredients and top with shaved Parmesan.