Season the chicken breast with half of the sea salt, black pepper, and dried oregano.
Heat a grill pan over medium-high heat and lightly brush with the olive oil.
Grill the chicken breast for 5 to 6 minutes per side until fully cooked, then remove from the pan and let rest for 3 minutes.
Place the halloumi slices on the hot grill pan and sear for 1 to 2 minutes per side until golden brown grill marks appear and the cheese softens.
Add the sliced zucchini and red bell pepper to the pan, grilling for 3 to 4 minutes until they are tender-crisp and slightly charred.
In a small bowl, whisk together the lemon juice with the remaining salt, pepper, and oregano to create a zesty dressing.
Toss the baby spinach with the lemon dressing in a large bowl, then top with the sliced grilled chicken, halloumi, and charred vegetables.