Heat a large skillet over medium-high heat and add the olive oil.
Add the diced chicken to the hot skillet and cook, stirring occasionally, for about 3 to 5 minutes until the pieces are about 70% cooked through.
Sprinkle half of the ranch seasoning mix evenly over the chicken and stir to coat.
Add the broccoli and diced zucchini to the skillet, then sprinkle the remaining ranch seasoning over the vegetables; drizzle the lemon juice and stir to combine.
Cover the skillet and steam the vegetables for about 3 minutes, until they are crisp-tender.
Uncover, add the spinach, and cook uncovered for about 1 minute, stirring occasionally, until the spinach is wilted and the chicken is cooked through.
Give everything a final stir and serve immediately.
