Begin by thoroughly rinsing your mung beans; we use a large stainless steel bowl and a sieve.
If you plan to puree using an immersion blender, bring the lentils, salt and water to a gentle boil in a larger dutch oven (so that any splatter stays in the pot). If you plan to use a blender, any kind of pot will do. Once the lentils are dancing around in the gentle boil, bring the entire dish to a medium-low simmer for about 20 minutes. Keep an eye to make sure that the lentil froth does not bubble over onto your stove; if it attempts to do so, lower your heat.
While the lentils are cooking, prepare your brussels sprouts by removing any damaged exterior leaves, washing the sprouts, and cutting them in half, length-wise. At this point, you may also begin heating up your oven; the temperature will need to be at 400 degrees for the sprouts to cook.
In a cast-iron pan, heat your olive oil until it shines; you will want enough olive oil to coat the bottom of the pan, and then a little bit more. The goal is not to burn the sprouts. Note: Don't forget to check on your lentils; if they are cooked, turn off the stove.
When the oil is hot, gently place your garlic slices and cut brussels sprouts, face-down, onto the heat. They will char quickly, maybe in two to three minutes, depending on your stove. Use a spatula to check the undersides after two minutes, just to make sure that they are not getting too brown.
When to bottom of the sprouts are a dark golden hue of your choosing, add another splash of olive oill and transfer the pan to the oven. Bake for about 10 minutes or until fully cooked.
By this point, the lentils should be fully cooked; turn off the stove. Use an immersion blender or counter blender to puree.