Heat the oil in a pressure cooker. Sauté the garlic for 30 seconds. Add the onion slices and sauté for 3-4 minutes.
Next add in mushroom slices and spinach and stir on high flame till spinach wilts.
Add 2 cups water to this along with stock cube (if using) and pressure cook* for 5 minutes (keep on sim for 5 min after 1 whistle). Remove and cool. Instant pot: high pressure manual setting for 4-5 minutes, then release steam.
Blend this to a smooth consistency once cooled.
Remove to a saucepan, bring to a simmer. Season with salt, pepper and dried oregano.
Check for salt. Add milk towards the end, bring it to a gentle simmer and transfer to bowls.
Garnish with a few salad greens, chia seeds, swirl of cream / coconut cream if you like.