In a saucepan, add the salt and sugar to the water, and simmer over moderate heat until salt and sugar are dissolved. Remove from heat, cool to room temperature, and add mushrooms to brine. Allow to marinate for at least 2 hours. Remove mushrooms from brine and gently press between towels to remove excess moisture. On a bbq or stovetop smoker over moderately low heat, gently smoke mushrooms until just cooked through. Set aside to add to finished chowder.
To make chowder, heat the olive oil in a deep soup pot. Add the onions, chipotles, and garlic. Saute until soft, but not brown, about 5 minutes. Add the tomatillos, fennel, cumin, coriander, oregano, cinnamon, tomatoes, and stock. Simmer gently for 15 minutes. Add the hominy to pot, and simmer to heat through. Correct the seasoning with salt and pepper.
To serve, slice the smoked portobellos at an angle, and place in warm soup bowls. Ladle the chowder on top and serve immediately.