1. Cut ends from each zucchini, slice zucchini in quarters lengthwise, then cut quarters in half crosswise. You'll have large pieces of zucchini about 2 to 3 inches long.
2. In heavy-bottomed skillet, warm olive oil and onion over medium-low heat until onion softens and becomes fragrant, 3 to 4 minutes. Add zucchini, garlic, lemon zest, 1 tsp salt, 1 tsp mint and 2 Tbsp water and stir well to combine. Reduce heat to low and cover. Cook, stirring occasionally, until zucchini is extremely tender and almost translucent, about 15 minutes. There should be some liquid in the bottom of the pan.
3. Remove lid, add lemon juice and increase heat to high. When liquid begins to bubble, remove from heat and set aside uncovered. When zucchini is at warm room temperature, stir in remaining 2 tsp mint and pine nuts, taste and add more salt and lemon juice if necessary. Serve warm or at room temperature.