In a medium saucepan, combine the sugar, lemon juice, and crushed mastic. Pour in 1 3/4 cups of water, set over high heat, and bring the mixture to a boil. Boil uncovered until the sugar has dissolved and the mixture is syrupy, about 8 minutes.
Add the figs, grapes, rose water, and cardamom seeds to the pan. Bring the mixture to a boil again, then turn down to a gentle simmer. Allow to simmer, uncovered, until thick and syrupy, about 25 minutes.
Meanwhile, in a dry skillet over low heat, gently toast the almonds, stirring occasionally, until they turn a couple of shades darker (any darker than honey and they’ve gone too far), 3 to 4 minutes. Tip into a bowl to cool and stop the cooking immediately.
Once the fig jam is thick and syrupy, stir in the toasted almonds and cook for 3 minutes more.
Remove jam from the heat. When cool, spoon it into a sterilized 18-ounce (500-ml) jar and cover with a lid. The jam will keep for a couple of months in a lidded jar, and for much longer in the fridge.