Heat olive oil over medium heat with a pinch of crushed red pepper. Add onions and cook until translucent, about 3 minutes. Add red bell pepper and continue to cook for 2 minutes. Add kale and cherries and continue to cook, while stirring, until kale is wilted but still vibrant green, about 3 minutes. Remove from heat and stir in red wine vinegar and honey, if using. Season to taste with salt and pepper. Enjoy immediately or pack for meal prep.