Prepare all ingredients into bite-sized pieces.
Add onion oil to a pan and preheat over medium-low heat.
Add the prepared onions and garlic, and sauté until they become translucent.
Add the base ingredients (tomatoes, celery, etc.) and stir-fry for 3-5 minutes.
When the vegetables are about halfway cooked, pour in water or stock.
Season with salt, pepper, and herbs, then simmer on low heat for 10 minutes.
Use the finished Onao base in your desired dishes.