1. Trim broccoli florets and stems to make 1/2" pieces.
2. Fill a large pot with a few inches of water and insert a steamer basket. Bring water to a simmer over medium-high heat. Add florets and stems; cover and steam 4-5 minutes, until tender-crisp. Remove from basket, run under cold water to cool.
3. Combine florets, stems, garlic, walnuts, Parmesan cheese, salt, pepper, olive oil and butter in a food processor. Pulse to process 10-15 times. Mixture should be slightly chunky and not pureed. Set aside.
4. Bring a large pot of salted water to a boil over high heat. Add pasta and cook according to package directions. Drain, let cool slightly. Return pasta to pot and add broccoli "pesto." Toss to coat.
5. Pour pasta onto serving platter and make a rectangle shape with pasta.
6. Cut two "eyes" from center of cucumber slices. Decorate rectangle with cucumber slices, olives, cherry tomatoes and avocado to create hair, mouth, horns, ears and a neck.