Zucchini, summer squash and portobello mushrooms are similar to eggplant in taste and texture. Eggplants are part of the nightshade family of plants, which includes tomatoes, bell peppers and potatoes.
Cooked eggplant generally has a uniform spongy texture and a neutral, slightly bitter flavor. This flavor and texture is comparable to varieties of squash such as zucchini and summer squash. SeriousEats.com notes that either of these vegetables make good eggplant substitutes in a traditional eggplant Parmesan recipe.
Eggplants come in many different varieties, though the American eggplant is most commonly available in the United States. Okra, portobello mushrooms or cocozelle may be used as cooking substitutes for this type of eggplant.