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1
Preheat oven to 375 degrees.
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2
1.
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3
Drain tuna either straight from the can or use a colander.
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4
Place tuna in a large mixing bowl; with a fork, break up the tuna so big chunks are separated and it has a flakey consistency.
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5
Set aside.
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6
2.
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7
Chop the onion, celery stalks (remove leafy steams), apple, and parsley.
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8
Try and chop each ingredient so they are relatively the same size, leaving the celery pieces slightly larger for extra crunch.
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9
3.
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10
Add the chopped vegetables to the tuna.
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11
3.
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12
Add mayonnaise to the bowl and fold ingredients together with a spatula.
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13
At this point, you can decide if you want to add more mayo; I look to see that the mixture is coated evenly with the mayo, but not drenched.
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14
4.
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15
Add 2 tablespoons of the mustard, salt, and pepper, and fold into the mixture.
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16
5.
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17
Slice English muffins in half, spread the remaining mustard on each of the four slices.
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18
6.
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19
Top the English muffins with equal amounts of the spinach, arugula, or watercress.
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20
7.
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21
Spoon equal amounts of tuna salad on top of the greens.
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22
8.
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23
Cut mozzarella cheese slices in half, and place on top.
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24
9.
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25
Place the sandwiches onto a baking sheet and place in the oven for 5 to 8 minuets, or until cheese is melted, golden brown, and bubbly.
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26
10.
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27
Enjoy!