While not always practical/feasible, try to establish a consistent schedule to stick to – one that sets aside time devoted to eating; even if it’s just something light like a can of chicken or tuna.
If you get a “lunch hour” and/or some type of breaks during the day, resist the urge to work through them, and make sure to eat instead.
Try making up an MRP drink that you can take to work in a large shaker bottle and sip throughout the day. MRP’s are a great way to get additional calories without the need to always stop and eat a solid meal.
Making your own is often better because you can doctor it up to your liking based on taste and nutrition.
Also: fats & oils are very important for muscle building and all around health - flaxseed, olive, wheat germ, canola oil's, etc. can all provide you with additional good calories without stuffing yourself with solid foods. A teaspoon of most good oils can contain around 125 calories. Taken 4 times throughout the day, that add's up to 500 extra quality calories.