Make the marmalade:
Trim the ends of the orange, halve it lengthwise, and slice it thin (about 1/8 inch). Bring the water and sugar to a boil and add the orange slices; simmer for 5 minutes. Let the mixture cool, cover the pan, and refrigerate for several hours or overnight. Drain the slices in a strainer or colander, discarding the liquid. Put the slices in a blender with 1/3 cup of the orange juice, the lemon juice, and the spices. Blend until completely puréed, about 30 seconds. Leave in the blender.
Put the remaining 1/3 cup orange juice in a small saucepan or a microwave-safe bowl. Sprinkle the gelatin over the juice and let swell and soften, about 3 min. Heat the mixture to melt the gelatin, about 2 min. on medium heat or 15 to 45 seconds in the microwave. Add the gelatin mixture to the blender and blend until it’s completely incorporated, about 15 seconds. Taste and add more spices and sugar, if necessary. Distribute the marmalade equally among the eight glasses you’re using to serve and chill.
Meanwhile, make the cream cheese mousse. Spoon equal amounts of the mousse over the marmalade in the glasses. Chill until needed, at least 30 minutes.
Make the streusel:
Put the butter in a bowl and add the rest of the ingredients one at a time, mixing until well blended after each addition. Chill until firm enough to crumble, about 1 hour in the refrigerator or 30 minutes in the freezer. Heat the oven to 350°F. Line a baking sheet with parchment. Crumble the streusel and sprinkle it evenly on a baking sheet. Bake until pale brown, about 14 minutes. Let cool.