Season the chicken. Pat the chicken dry.
Season generously with salt, pepper, and the dried oregano. This quick step builds flavor from the start.
Brown the chicken. Heat the olive oil in a large, deep skillet or Dutch oven over medium-high heat. Add the chicken in a single layer and sear for 3–4 minutes per side until lightly golden.
Remove to a plate; it will finish cooking later.
Sauté the aromatics. Reduce heat to medium. Add the onion and a pinch of salt. Cook 3–4 minutes until translucent, then stir in the garlic for 30 seconds until fragrant.
Don’t let it brown.
Toast the orzo. Stir in the dry orzo and cook for 1–2 minutes, coating it in the oil and aromatics. Light toasting deepens flavor and helps the orzo keep some bite.
Deglaze and simmer. Pour in the chicken broth, scraping up any browned bits. Add the lemon zest and red pepper flakes if using.
Bring to a gentle simmer.
Add chicken back. Return the seared chicken and any juices to the pot. Reduce heat to medium-low and cook, stirring occasionally, for 8–10 minutes until the orzo is tender and the chicken is cooked through.
Finish with lemon and add-ins. Stir in the lemon juice and peas, and cook 1–2 more minutes. If using Parmesan, add it now for creaminess.
Adjust salt and pepper to taste.
Adjust texture. If the orzo has thickened too much, splash in a bit more broth or hot water to loosen. It should be creamy but spoonable.
Top and serve. Remove from heat and fold in the fresh parsley or dill. Taste again and add a final squeeze of lemon if you like it extra bright.