Copycat Panera Bread Strawberry Poppyseed Salad

Name: Copycat Panera Bread Strawberry Poppyseed Salad
Ingredients: 2 boneless, skinless chicken breasts (about 1 lb. total); 1 tsp. sodium-free lemon pepper; Kosher salt; 2 tbsp. distilled white vinegar; 1/2 tsp. finely grated orange zest; 1 tbsp. fresh orange juice; 1 tsp. Dijon mustard; 1 tsp. poppy seeds; 3/4 tsp. granulated sugar; 1/2 tsp. dried minced onions; 1/3 c. vegetable oil; 1 (10-oz.) head romaine, chopped (about 6 c.); 1 (10.5 oz.-can) Mandarin oranges in light syrup, drained; 3/4 c. pineapple chunks; 3/4 c. strawberries, quartered; 1/2 c. blueberries; 1/3 c. toasted pecans, roughly chopped