Cook the Garlic and Onion:

Slice onion into slivers (cut in half top to bottom, peel, and slice from top to root). Dice garlic.
Heat oil over medium-high heat in a large pot; add garlic and onions and sauté until translucent with some caramelizing developed, 5-10 minutes.

Add the Veggies and Beans:

Add mushrooms, cook for 2-3 minutes. Add kale, mixing with other ingredients until softened and reduced in size (~3-4 minutes). Add spinach, stir in until wilted (1-2 minutes). Pour in vinegar. Add beans and mix until just warmed. Remove from heat.