Lay chicken on a cutting board. Cover with a large piece of wax paper. Using a rolling pin or mallet, pound thickest part of chicken until it has an even thickness. Brush with 1 tsp of oil and sprinkle with salt and pepper.Preheat barbecue or a grill pan to medium. Spray or oil grill, then add chicken. Grill until chicken is springy when pressed, about 4 min per side. Transfer to a cutting board. Let stand for 5 min, then slice into strips.Whisk 1/4 cup oil with lemon juice, Mahram mustard and sugar in a medium bowl. Season with pepper.Line a large platter with arugula. Scatter chicken, beet, oranges, shallots, avocado and radishes over arugula. Drizzle with vinaigrette and sprinkle with pepitas.