Make the pudding according to the package instructions. Add the cinnamon, orange zest, and red pepper flakes before chilling in a large trifle dish. Before serving, sprinkle the top with chopped Candied Orange Peel.
Candied Orange Peel: Using a vegetable peeler cut the orange part of the peel from the stem end of the orange down to the navel end, forming long 1-2cm strips. Bring a heavy small saucepan of water to a boil. Add the peels and cook for 1 minute. Drain and then rinse the peels under cold water. Repeat cooking the peels in the saucepan with fresh boiling water and rinsing under cold water 2 more times.
Stir the sugar and 115ml of fresh water in a heavy small saucepan over medium-high heat until the sugar dissolves. Bring to a boil. Add the orange peels and simmer over medium-low heat until tender, about 15 minutes. Using tongs, transfer the peels to a sheet of parchment paper to dry slightly, about 1 hour.