Peel and chop the garlic.
Add the can of fire-roasted tomatoes, can of tomatoes with chilies, can of tomato paste, the vegetable stock, dry mung beans, and garlic to the slow cooker. Stir these ingredients together well. Turn the slow cooker on high and set it to cook for 2 hours.
Meanwhile, add garam masala to a small frying pan and roast over a low flame, stirring constantly for about 2-3 minutes. When it begins to smell a bit more pungent, take it off the stove and set it aside on a plate.
Then, peel and chop the onions. Add some olive oil to the same frying pan and add the onions to it. Let the onions saute over a low flame, stirring often. When they caramelize (about 20-25 minutes), turn the stove off and set the onions aside.
Drain and rinse the canned black beans and canned chickpeas.
When the 2 hours of cooking time are up, uncover the slow cooker and add the roasted garam masala, the caramelized onions, the cocoa, the drained and rinsed chickpeas, and the black beans. Place the lid on and let it cook on low for another hour and fifteen minutes.
Turn off the slow cooker, season this stew with salt and black pepper to taste, garnish it with some fresh herbs, such as parsley or cilantro, and enjoy!