In a large bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, smoked paprika, salt, and black pepper. Add the cubed chicken breast to the bowl, tossing to coat evenly.

Cover the bowl and refrigerate for at least 30 minutes, or up to 2 hours for best flavor. If using wooden skewers, soak them in water during this time to prevent burning on the grill.

While the chicken marinates, cut the bell peppers and red onion into roughly 1-inch pieces, similar in size to your chicken cubes. This ensures they cook evenly alongside the chicken.

Thread the marinated chicken and prepared vegetables alternately onto the skewers. Don't pack them too tightly; leaving a little space helps them cook evenly and allows for better charring.

Preheat your grill to medium-high heat (about 400-450°F or 200-230°C). Lightly oil the grill grates using a paper towel dipped in a little oil to prevent sticking.

Place the skewers on the hot grill. Cook for 10-15 minutes, turning every 3-4 minutes, until the chicken is cooked through (internal temperature reaches 165°F or 74°C) and has nice char marks on all sides. The vegetables should be tender-crisp.

Carefully remove the skewers from the grill and let them rest for 5 minutes before serving. This helps the juices redistribute, keeping the chicken moist and tender. Serve hot.