Preheat the oven to 400°F (200°C).

In a large skillet, heat olive oil over medium heat. Add the diced onion and minced garlic, sauté until translucent.

Add carrots, celery, green beans, and corn. Cook for about 5 minutes, stirring occasionally.

Pour in the vegetable broth, thyme, salt, and pepper. Bring to a simmer and cook for another 5 minutes.

Remove from heat and transfer the vegetable mixture to a greased casserole dish.

In a mixing bowl, combine flour, baking powder, and salt.

Cut in the cold butter until the mixture resembles coarse crumbs.

Stir in the milk until just combined. Do not overmix.

Drop spoonfuls of the biscuit dough over the vegetable filling in the casserole dish.

Bake in the preheated oven for 25-30 minutes, or until the biscuit topping is golden brown.

Remove from the oven and let cool for a few minutes before serving.