Rinse chicken inside and out; let drain on a tilted plate for 10 minutes, then pat dry with paper towels.
Roll lemons on the counter to soften them.
Roughly chop onions. Mince garlic cloves.
Cut everything bagels into bite-sized cubes.
Chop romaine lettuce. Thinly slice cucumber, radishes, and red onion.
Halve cherry tomatoes. Roughly chop parsley and mint.
If using avocado, dice or slice. Grate or mash the garlic for the vinaigrette.