In a large pot, heat the olive oil over medium heat. Add the chopped onion and sauté for about 5 minutes until translucent.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the sliced carrots and celery, cooking for another 5 minutes until they begin to soften.
Incorporate the diced zucchini, yellow squash, and red bell pepper. Sprinkle in the thyme, basil, salt, and pepper. Cook for 5 more minutes, stirring occasionally.
Pour in the vegetable broth and bring the mixture to a boil. Reduce heat and let it simmer for 15 minutes until all vegetables are tender.
Stir in the heavy cream, frozen peas, and chopped spinach. Cook for an additional 5 minutes until heated through.
Remove from heat and stir in the lemon juice before serving.