In a 2-quart saucepan, combine tomatoes, plums, green onions, brown sugar, vinegar, chile pepper, lemon peel and juice, curry powder, and cardamom. Bring boiling; reduce heat. Simmer, uncovered, for 30 to 35 minutes or until slightly thickened, stirring frequently. Remove from heat; cool to room temperature.
Transfer the chutney to a covered container and chill in the refrigerator for at least 8 hours before serving. Makes about 2 cups.
To seed tomatoes, quarter each one and scoop out the seeds with a small spoon.
Store, tightly covered, in the refrigerator up to 1 week or in the freezer up to 3 months.
Chutney may also be served with beef, lamb, pork, sausage, or poultry.