In an 8-quart saucepot, heat olive oil on medium. Add salt, celery, shallots, and garlic. Cook 8 minutes or until golden, stirring. Add broth and broccoli. Heat to simmering on high. Reduce heat to medium-low; simmer 15 minutes, stirring occasionally. Add spinach, mushrooms and orzo. Simmer 8 to 10 minutes or until starches and veggies are softened. Remove from heat. Stir in basil pesto to taste.