Heat olive oil in a large saute pan over medium-high heat until shimmering.

Add diced onion, carrot, celery, minced garlic, thyme leaves, and bay leaf.

Saute until the onion turns translucent.

Add zucchini and summer squash; season with salt and pepper.

Stir to coat vegetables with the onion mixture.

Sprinkle diced red bell pepper over the squash.

Reduce heat to medium-low.

Cover and cook until vegetables are tender, approximately 20 minutes.

Transfer stew to a serving dish.

Garnish with chopped fresh basil.