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.