Heat oil in a large skillet over medium-high heat.
Add chicken, bell pepper, salt and pepper; cook, stirring occasionally, until the chicken is just cooked through, 7 to 9 minutes.
Add garlic and cook, stirring, until fragrant, about 1 minute.
Whisk wine and cornstarch together in a measuring cup.
Add to the pan along with the lemon juice and zest; stir to coat, then bring to a simmer.
Add spinach by the handful; cook, stirring, until wilted, about 2 minutes more.
Serve sprinkled with Parmesan.
