Heat olive oil in a large skillet or wok over medium-high heat.
Season chicken cubes with salt, pepper, and oregano, then sauté until golden brown and cooked through.
Remove chicken from the skillet and set aside.
In the same skillet, add garlic, zucchini, and bell pepper; sauté for 3-5 minutes until crisp-tender.
Add the dried orzo to the skillet and stir for 1 minute to lightly toast.
Pour in chicken broth and bring to a simmer.
Reduce heat to low, cover, and cook for 8-10 minutes until the liquid is absorbed and orzo is tender.
Stir the cooked chicken and baby spinach into the orzo until the spinach is wilted.
Finish by stirring in the lemon juice and lemon zest, adjusting seasoning to taste before serving.