Heat the oil in a pot or large saucepan over medium-high heat.
Sauté onion, celery and carrot until softened.
Add butter, garlic and oats and cook, stirring, for about a minute to toast oats.
Add stock and stir until nearly absorbed.
Stir in corn, green beans, milk, thyme, salt and pepper.
Bring to a simmer and cook, uncovered, for 5 minutes.
Remove from heat, taste and adjust seasonings.
Let stand for 5 minutes and stir before serving. (Soup will continue to thicken.)
Note: if you used fresh thyme, don’t forget to remove the stems before serving!