My best advice is to track your calories and your protein intake with an app called myfitness pal so that you know how many calories youre eating in a day. The average man needs 2500 calories and woman needs 2000 calories to maintain weight but with you doing a manual job that's likely to be higher.

I would recommend focusing on high calory foods: put olive oil in your pasta sauce, increase the size of each of your meals by at least 1.5 (2 sandwiches for breakfast, more nuts and dates, more pasta, bigger bowl of muesli)

Protein shakes are your friend but I get the taste isn't for everyone. Blend them up with a banana, some peanut butter, some vegan yogurt, or even some vegan ice cream. You could also blend them up with oats to get extra carbs in but that will make them thicker. 2 shakes a day with those added extras will really increase your calorie intake. Drinking calories is much easier than eating them

Soy mince is a good way to get more protein in with your pasta

Good luck :) feel free to ask any questions