Sprinke 1 teaspoon of salt over the eggplant pieces, stir, and let sit for 6-8 minutes. Meanwhile, in a large, heavy skillet or stew pot, saute onions and garlic in moderately hot oil until golden brown, stirring and watching carefully to prevent scorching. Add all the spices and the pepper, and continue to stir for another couple minutes.
Squeeze eggplant pieces between your fingers, or press them firmly with a fork, to squeeze out excess moisture. Then gather them into a clean, lintfree cloth and gently squeeze again. Dump pieces into the pot. Stir unitil eggplant becomes limp and slightly golden, adding a bit more oil if necessary. Then add potatoes and let them brown on all sides.
When potatoes are somewhat tender, but still resistant to a fork, add tomatoes, tomato sauce and 1 1/2 cups of water, Stir, bring to a boil, then reduce heat and simmer until vegetables are tender but not mushy. The sauce should be thick, like syrup, rather than watery. If it isn't, simmer a little longer, stirring as necessary to prevent sticking. If it's too thick, add more water. Serve over rice.