Combine all of the ingredients for the pesto in a food processor and pulse until completely blended. Taste and season with salt and pepper and set aside.
Cook the Fennel and Tomatoes:
Heat 2 teaspoons oil in a wide pot over medium-high heat. Add the fennel and cook, stirring occasionally for 6-7 minutes until it begins to brown around the edges. Add the tomatoes and cook an additional 5 minutes until they begin to soften but not completely break down. Season with salt and pepper. Transfer to a bowl.
Cook the Leeks:
Melt the butter into the pot and add the leeks. Cook for 4-5 minutes until softened.
Cook the Couscous:
Add the pearl couscous to the leeks and cook for 1-2 minutes until it just begins to toast and turn golden brown.
Simmer the Pearl Couscous:
Pour in the vegetable stock and bring to a boil. Reduce heat and simmer for 15 minutes until the couscous is tender. Season with salt, pepper, and crushed red pepper to taste.
Finish the Couscous:
Pour in the pistachio pesto and toss to coat. Fold in the fennel and tomatoes and toss gently to coat everything with the pesto. Taste and season once again to taste. Turn off the heat.
To Serve:
Divide the pearl couscous between bowls and garnish with the reserved herbs – a few basil leaves, a few sprigs a dill, a few fennel fronds, and a couple parsley leaves. Drizzle with a touch of extra virgin olive oil, if you like. Enjoy!