Into a purchased jello brain mold, layer your shrimp in, tails facing the middle of the brain. It's best if you layer them into the brain mold with the tails facing the middle, according to each "hemisphere" of the brain. This will give you the most realistic look. Tuck the shrimps in close together.
Drop bits of roasted pepper and green onion in around the shrimp. These should look like veins and nerves when you're finished.
Repeat, alternating between shrimp and vegetables, until you fill your Jello brain mold.
Now make the gelatin. In a small saucepan, bring the chicken broth to a boil. Remove from heat and stir in the unflavored gelatin.
Stir in the lemon zest, juice, tomato paste, garlic, honey, Cajun seasoning, and a pinch of salt (the amount will depend on how much salt is in your Cajun seasoning-- mine's salty so I don't use much).
Pour this mixture over the shrimp in your brain mold, filling to the top. Discard any extra. With a rubber spatula, smooth the top of your shrimp and gelatin to create a smooth surface.
Refrigerate until firm, at least several hours.
To unmold, set your Jello brain mold in a bowl of hot water for a few seconds. Place a serving tray underneath, then flip your mold over. The brain should pop right out. This is one of the easiest gross Halloween foods to make in advance!