Cook onion in 2 tbsp. oil in a large frying pan over medium heat, stirring, until deep golden brown, about 15 minutes; transfer to a bowl as cooked and season with salt.
Trim okra stems without piercing pods (leave a bit of stem on).
Mix 1/2 tsp. salt and the spices (but not lemon juice, if using) in a bowl. Slit each okra pod lengthwise from just below stem to 1/2 in. from tip. Poke a finger into slit to hold it open and stuff with some spices.
Add okra and remaining oil to pan. Cook over medium heat until lightly browned, 5 minutes, tipping pan occasionally. Add 1/2 cup water and lemon juice, if using; quickly cover and simmer until okra is tender-crisp, 5 minutes. Toss gently with onion.
*Buy in Indian markets or at worldspice.com.
Note: Nutritional analysis is per serving.