Start by cleaning and cutting the chicken breasts into 1-inch cubes. This size ensures even cooking and easier threading onto the skewers. Next, whisk together olive oil, fresh lemon juice, minced garlic, salt, and pepper in a bowl. Add the chicken cubes and toss until well coated. Allow the chicken to marinate for at least 15 minutes, though leaving it longer (up to 2 hours) will infuse even more flavor.
While the chicken marinates, soak your wooden skewers in water for about 30 minutes. This is a crucial step to prevent the skewers from burning during grilling. Slice bell peppers and onions into similarly-sized chunks for uniform cooking.
Preheat your grill to medium-high heat. Thread the chicken pieces onto the skewers, alternating with chopped vegetables for a pop of color and texture. Place the skewers on the preheated grill and cook for about 5-7 minutes per side. Turn them occasionally to get a nice, even char. The internal temperature of the chicken should reach 165°F before serving.
Once the skewers are off the grill, allow them to rest for a couple of minutes. This helps retain the juices in the chicken. Serve them hot and enjoy the explosion of flavors in every bite!