In a bowl, whisk together garlic powder, dried oregano, lemon juice, olive oil, salt, and black pepper.
Add chicken breast and coat evenly with the marinade.
Preheat a grill or griddle pan over medium heat.
Grill the chicken until fully cooked, reaching an internal temperature of 165°F (74°C). Remove from heat and allow to rest briefly.
Lightly grill or toast buns until golden.
Spread mayonnaise on the inside of each bun.
Layer with lettuce, tomato, grilled chicken, Swiss cheese, and red onion.
Combine sparkling water, lemon slices, and chia seeds. Stir thoroughly, let rest briefly, then stir again to prevent clumping.
Serve the sandwich with carrots and hummus, blueberries, and lemon sparkling water with chia seeds.