Place the potatoes in a saucepan, add in the salt. Pour enough water to cover the potatoes at an inch in depth. Boil the potatoes on high heat for 20 to 25 minutes or until the potatoes are tender. To check if the potatoes are ready, insert a skewer into the middle of it, it should pierce through with little pressure. Leave the water in the saucepan and transfer the potatoes onto a cooling rack or colander. Leave for 10 minutes to allow the steam to dry the potatoes.
Add the peas into the same saucepan and cook over high heat for 2 minutes. Drain the peas and set them aside.
Cut the potatoes into quarters or bite-size portions. In a food processor or blender, add in the sour cream, mayonnaise, horseradish, garlic, mint, chives, salt and 1.5 cups of peas (leave the remaining peas to add on top of salad). Blend the dressing ingredients together until it's smooth and well combined. Gently mix the potatoes and dressing in a large bowl. Give it a taste and add salt and pepper if needed.
Slice the halloumi into 1cm in thickness. Brush a nonstick frying pan or grill plate with olive oil and heat it up on medium heat. Add in the halloumi and cook for 3 to 4 minutes on each side or until golden.
To serve, place the potatoes on a large plate, add the remaining peas and halloumi on top. Garnish with mint leaves.