In a large pot, heat oil over medium heat. Add vegetable scraps (frozen is fine, no need to thaw first) and cook for a few minutes.
Crush garlic cloves (peels may be left on, but feel free to remove them if you prefer). Add them to pot along with herbs, bay leaf, and corriander seeds. Fill pot with enough water to cover the vegetables by one inch. Stir in salt and pepper.
Bring pot to a simmer over medium heat. Cover, reduce heat to low, and continue simmering for at least 40 minutes (longer times will further concentrate the broth, though may reduce your final volume). Sample the broth during the last 10 minutes, and adjust the salt to your liking, if needed.
Remove from heat. Strain the broth to remove the scraps and other solids. Broth may be used immediately, or it can be stored in the refrigerator for up to 3 days prior to use.