Pound each chicken breast to an even thickness so they cook evenly, then place the breasts in a gallon freezer bag or a shallow pan.
In a mixing bowl, whisk together the olive oil, lemon juice, Dijon mustard, honey, dried minced onion, oregano, paprika, minced garlic, cayenne, salt, and black pepper until smooth.
Pour the marinade over the chicken in the bag or pan, seal or cover, and refrigerate for a few hours or up to overnight.
When ready to cook, preheat your grill or grill pan to medium-high heat.
Remove chicken from the marinade, letting excess drip off, and grill or pan-sear until an instant-read thermometer inserted into the thickest part registers 165°F (about 6–8 minutes per side depending on thickness).
Transfer the cooked chicken to a plate and let rest a few minutes before serving.
