Measure the lentils and then sprinkle them slowly into a mesh strainer; watch carefully for dirt, pebbles, or other debris. Once you’ve added all of the lentils to the strainer, pick through them making sure you didn’t miss anything.
Add the measured rice to the same strainer and rinse the lentils and rice well under cold running water. Drain while you continue with the recipe.
Heat the oil in a large skillet over medium-high heat with a bit of onion. When it begins to gently sizzle, add the remaining onion and mushrooms. Cook, stirring often, for about 5 minutes or until softened. Add the carrots and cook while stirring for about 30 more seconds. Scrape everything from the skillet into a large bowl and set aside.
Put the lentils/rice, broth, and tomatillo salsa into the same skillet over medium-high heat and bring to a simmer. Reduce the heat and cover. Adjust the heat, if necessary, to keep at a simmer.
Cook the lentils/rice for 25 minutes. Stir, shake the pan so the contents even out, and recover. Cook for another 25 minutes.
Uncover the pan and mash well using a potato masher; some of the lentils and rice will remain intact and that's just fine. Continue to cook, while stirring, for about 5 more minutes or until the excess liquid is evaporated.
Remove from heat and stir for a few minutes so the steam evaporates and the lentils/rice cool down. The idea is to end up with a cooked, mashed, and fairly dry lentil/rice mixture.
Transfer the lentil/rice mixture to the bowl with the cooked veggies; add the pumpkin seeds, flour and spices. Stir well with a large spoon; the batter should be fairly stiff (if necessary, add more garbanzo bean flour, one Tablespoon at a time). Transfer the batter to a cutting board.
Using your hands, shape the batter into an even mound. Cut the mound in half, then cut each half into three equal-sized pieces. Shape each of these six pieces into a thick patty. Secure the edges of the patties by pressing them with the flat edge of a large butter knife.