There are many delicious side dishes that pair well with leg of lamb. Here are some ideas from various sources:

From The Happier Homemaker:

• Slow Cooker Au Gratin Potatoes
• Classic Green Bean Casserole
• Grilled Corn on the Cob

From Food52:

• Shaved Asparagus & Arugula Salad
• Radish Salad With Anchovy Sauce
• Sweet Potato Wedges with Coconut Oil

From The Spruce Eats:

• Potatoes Grand Mere
• Garlic and Thyme Spring Vegetables
• Simple Roasted Brussels Sprouts

From Sainsburys:

• Dijon Mustard Glazed Carrots
• Herby Roasted Jersey Royals
• Zesty Spring Greens

From Bake It With Love:

• Dauphinoise Potatoes
• Roasted Asparagus and Cherry Tomatoes
• Honey Glazed Oven Roasted Carrots

From Delish:

• Bacon Pea Salad
• Air Fryer Asparagus
• Greek Lemon Potatoes

Some other ideas include:

• Roasted root vegetables (such as carrots, parsnips, and sweet potatoes)
• Grilled or roasted asparagus
• Ratatouille
• Creamed spinach
• Minted peas
• Couscous or quinoa salad
• Roasted garlic mashed potatoes

Ultimately, the best side dishes for leg of lamb will depend on personal preference and the specific seasoning and cooking method used for the lamb.