Step 1: Prep the Ingredients

1. Dice the onion and mince the garlic.
2. Chop the carrots and celery into bite-sized pieces.
3. Peel and cube the potatoes.

Step 2: Sauté the Aromatics

1. Heat olive oil in a large soup pot over medium heat.
2. Add the onion and garlic, cooking until fragrant, about 2 minutes.
3. Stir in the carrots and celery, sautéing for 5 minutes until softened.

Step 3: Add the Main Ingredients

1. Add the potatoes, lentils, rosemary, thyme, Dijon mustard, soy sauce, and brown sugar.
2. Pour in the vegetable broth and stir well.

Step 4: Simmer the Stew

1. Cover the pot and bring to a boil over high heat.
2. Reduce heat to low and simmer for 30 minutes, stirring occasionally, until the lentils and potatoes are tender.

Step 5: Mash for Texture

1. Use a potato masher to gently mash some of the potatoes directly in the pot.
2. This step thickens the stew while keeping it hearty.

Step 6: Add the Finishing Touches

1. Stir in the frozen peas and let them heat through for 5 minutes.
2. Taste and adjust the seasoning with salt and pepper.

Step 7: Serve

1. Ladle the stew into bowls and garnish with fresh herbs, such as cilantro or parsley.
2. Pair with crusty bread or pita for a complete meal.