Finely dice the onion and mince the garlic; have all ingredients measured and ready.
Heat olive oil in a large nonstick pot over medium-high heat. Add the diced onion and cook, stirring, until golden, about 5 minutes.
Add the minced garlic and stir for about 30 seconds, then add the ground turkey. Season with salt and pepper and cook, breaking up the meat, until mostly cooked through, about 5 minutes.
Add the frozen corn and frozen peas (no need to thaw) and stir 1–2 minutes until the vegetables are thawed and the meat is fully cooked. Transfer this mixture to a plate or bowl and cover with foil.
Return the pot to the heat and melt the butter. Whisk in the flour and cook, stirring, for 1 minute to form a roux.
Gradually whisk in the chicken stock, then stir in the whole milk and add the uncooked orzo.
Bring to a simmer, then reduce heat to maintain a gentle edge-of-simmer. Cook uncovered for about 7 minutes, stirring occasionally and scraping the pot so the orzo does not stick; the mixture should be slightly soupy and the orzo almost tender.
Return the cooked meat and vegetables to the pot and stir to combine. Add the grated Parmesan and stir until melted.
Stir in the basil pesto and optional parsley. Taste and adjust salt and pepper as needed. If too thick, add a splash of milk to reach a creamy, risotto-like consistency.
Serve immediately while hot.