Before starting, wash and dry all produce.Lightly oil the grill. While you prep, preheat the grill to 500°F over medium-high heat. Thinly slice cucumber into rounds. Peel, then cut onion into ½-inch rounds (keeping rings together). Cut ciabatta into 1/2-inch-thick slices. Transfer onions and ciabatta slices to a plate. Brush with 1 tbsp oil (dbl for 4 ppl). Season with salt and pepper. Add half the maple syrup and half the mustard to a medium bowl. Stir to combine. (NOTE: This is your maple-mustard sauce.)

Add vinegar, remaining maple syrup, remaining mustard and 1 tbsp oil (dbl for 4 ppl) to a large bowl. Season with salt and pepper, then whisk to combine. Add cucumbers, then toss to coat. Set aside.

Pat chicken dry with paper towels. Season with chicken salt and pepper. Drizzle 1/2 tbsp oil (dbl for 4 ppl) over top. Add chicken to one side of the grill. Close lid and grill, flipping once, until chicken is cooked through, 4-5 min per side.** When chicken is cooked through, brush one side with maple-mustard sauce, then flip. Grill for 30 sec, then repeat on the other side. Transfer chicken to the same medium bowl with any remaining maple-mustard sauce, then toss to coat.

Meanwhile, add onions to the other side of the grill. Close lid and grill, flipping once, until tender, 5-7 min per side. Meanwhile, add ciabatta slices to the grill. Close lid and grill until ciabatta is crisp and grill marks form, 2-3 min per side. Transfer onions and grilled ciabatta to a plate to cool.

Cut cooled ciabatta into 1/2-inch pieces. Add spinach and half the croutons to the large bowl with cucumbers. Season with salt and pepper, then toss to combine. Separate onion rings. If desired, cut onions into bite-sized pieces.

Divide salad between plates. Top with remaining croutons, onions, chicken and any remaining sauce from the bowl. Sprinkle with salad topping mix.